No Option For Graphics CPU in Render Settings
Now you must have Blender Render on that renderer option of yours.
Change it to cycles! Now! Now!

The option box on the render setting will magically appear!



Additional Notes
You may need to make sure the Performance numbers are setup correctly
to make rendering go faster when you are using the GPU. Also beware
that overly bright scene that renders with lots of "firefly" noise
will slow down the render too.


Turn on "Auto Tile Size" in your user preference add on tab.





Here is where you will find the tool on the performance header.